Interaction betweenCu–S-Based Sphalerite-likeFrameworks and Interstitial Cations in Colusite-Based ThermoelectricMaterials

Cu–S-based multicomponent compounds with sphalerite-like frameworks have garnered attention as midtemperature p-type thermoelectric (TE) materials. Their valence bands, primarily comprising Cu–S hybridized orbitals, control electronic properties. Herein, for colusites Cu₂₆Tr₂M₆S₃₂ (Tr = V, Nb, and Ta; M = Ge and Sn), we investigate the distinctive interaction between the Cu–S-based sphalerite-like framework and Tr at the interstitial tetrahedral sites to improve the Seebeck coefficient (<i>S</i>). According to ab initio calculations, the d(<i>t</i>₂) and d(<i>e</i>) orbitals of Tr interact with the valence band maxima at the Γ and M points, respectively. The hybridization between the Tr-<i>t</i>₂ and S orbitals (under the presence of Tr), along with structural modifications, reduces the energy of the Γ band maximum toward the Fermi level, thereby increasing <i>S</i>. This understanding is expected to be a foundation for further advancements in the TE properties of Cu–S-based compounds.